Studies of electrochemical cells have been enthusiastically made in recent years. For example, a fuel cell among electrochemical cells includes a system configured to electrochemically react with the fuel such as hydrogen with an oxidizer such as oxygen to generate electric power. Among these fuel cells, a polymer electrolyte membrane fuel cell (PEFC) is operable at a lower temperature than other fuel cells and produces water as a reaction product so that it is clean to environment and has been therefore put to practical use as power sources for household stationary use and for vehicles.
In a catalyst layer contained in each electrode of PEFC, a carbon-supported catalyst obtained by supporting a catalyst material on a carbon black support is generally used.
When PEFC is used, for example, as a power source for vehicles, the carbon support contained in the catalyst layer is corroded by start and stop operations, and also, the catalyst supported on the carbon support is itself also dissolved. It is reported that this promotes the deterioration of the catalyst layer and the membrane electrode assembly (MEA) including the catalyst layer. For this, it is desired to improve the durability of the catalyst layer.
In light of this, the adoption of a carbonless catalyst layer formed by sputtering or vapor deposition of catalyst material is examined. For example, there is a catalyst layer obtained by sputtering a whisker substrate with platinum. There is also a catalyst layer including a void layer obtained by stacking a catalyst material layer and a pore-forming material layer alternately on each other and then, by dissolving/removing the pore-forming material layer. The deterioration of the catalyst support caused by corrosion can be avoided by the use of the carbonless catalyst layer like this. However, the resistance of these catalysts to dissolution is still insufficient and therefore needs to be further improved.